The study is carried out to clear the phenomenon of the flow of self-shiphonage, which is the main cause of the water seal loss in the trap. The drainage system for the experiments are attached an S trap to each sanitary fixture. The experiments were performed by changing some factors which seem to have influences on the characteristics of the drainage flow, and carried out for the case of washing in filled water and washing with running water. The influences fo these factors are qualitatively analyzed, and the phenomenon of the flow just before the finish of discharge was analyzed by the experiments which an S trap is attached to the sanitary fixture. This report is suggested four actual models of the discharge flow, as follows ; (1) the case of generating the initial water head in the inlet of the trap. (model 1) (2) the case of the inflow equal to discharge. (model 2) (3) the case of generating the initial water head by return water from the weir of the trap. (mode 13) (4) the case of the plug flow is occured just before the finish of discharge. (model 4) Depending on assuming those models, the authors consider that a theoretically analysis will be able to be produced in future.